Ajust thank you page when contribution on mobile

It closes #346.

### Before
![screen shot 2014-06-09 at 12 11 54 pm](https://cloud.githubusercontent.com/assets/230476/3215893/1f9bd9f6-efc7-11e3-96e9-d6b768b6dc4a.png)

### After
![screen shot 2014-06-09 at 12 12 31 pm](https://cloud.githubusercontent.com/assets/230476/3215894/1fc808f0-efc7-11e3-9440-96ca17785d10.png)